1. Field of the Invention
The present invention relates to the use of certain silane-grafted amorphous poly-.alpha.-olefins as a moisture-crosslinking adhesive base material or as a constituent of a moisture-crosslinking adhesive system, especially for applications in the construction, woodworking and automotive industry, where the adhesive is used primarily as a hotmelt adhesive.
2. Description of the Background
Amorphous poly-.alpha.-olefins are used as adhesive base materials for a wide range of applications. The field of use extends from the hygiene sector through laminates and packaging adhesives to constructive bonding and uses in wood processing. In the majority of these applications, the adhesive base materials are notable for their strong adhesion to various substrates, strong cohesion and good resistance to chemicals coupled with an excellent price/performance ratio.
Many demanding applications, for example the bonding of glass, ceramic, metal and various polymer combinations, can be realized to a certain extent by amorphous poly-.alpha.-olefins by formulating the adhesive base material with a large number of components and additives such as tackier resins, waxes, other polymers, plasticizers and stabilizers. Nevertheless, it is not possible in every case to attain the required levels of adhesion and cohesion. Furthermore, the thermal stability of adhesive bonds implemented with amorphous poly-.alpha.-olefins or with formulations based on these substances is inadequate for certain applications, so that in many cases the user has to resort to more expensive, reactive bonding systems, such as polyurethane, epoxy or silicone adhesives.
DE 40 00 695 describes amorphous poly-.alpha.-olefins onto which are grafted reactive monomers and which are employed as hotmelt adhesives and for heavy-duty carpet coating compositions. Because of the low level of molecular non-uniformity dictated by their preparation, these grafted poly-.alpha.-olefins possess improved cohesion. For heavy-duty bonding, however, the cohesion thus obtained is still inadequate. Furthermore, no marked improvements are achieved with respect to thermal stability.
In order to improve the cohesion and the thermal stability of the adhesive film, it is also necessary for chemical bonds to be formed between the polymer chains of the adhesive film. Such a system is described in DE 195 16 457. The system described therein, however, consists of two different polymer components, one being a silane-grafted polyolefin such as ethylene-vinyl acetate (EVA) copolymer and the other being a maleic anhydride(MAA)grafted polyolefin (e.g. EVA) to which a crosslinking accelerator is added. The handling of this multicomponent system is labor-intensive because of the two components, which are absolutely essential, and the resulting logistical and mixing effort. Furthermore, the toxicological properties of MAA-grafted systems make them unsuitable for use in the food sector, which is a limitation which further restricts the scope for employing the system disclosed and claimed in the reference. A need continues to exist for adhesive compositions based on poly-.alpha.-olefins which not only exhibit good adhesive properties, but which also exhibit good thermal stability.